Treatment of diabetes with synthetic beta cells

ABSTRACT

Disclosed is a method for obtaining glucose-regulated expression of active insulin in the cells of a mammalian subject. The method involves delivering into the subject a genetic construct comprising a coding sequence for a human proinsulin operably connected a promoter functional in the host cells. The construct includes a glucose responsive regulatory module having at least one glucose inducible regulatory element comprising a pair of CACGTG motifs linked by a five base nucleotide sequence, which confers glucose inducible expression of the proinsulin coding sequence. To ensure proper processing of the proinsulin to active insulin, the coding sequence was modified to direct the synthesis of a mutant proinsulin polypeptide having amino acid sequences that can be cleaved to mature insulin in suitable host cells, such as hepatocytes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.09/115,888, filed Jul. 15, 1998, which is a continuation-in-part ofapplication Ser. No. 08/786,625 filed Jan. 21, 1997, now abandoned.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with United States government support awarded byNIH, Grant Nos: R01 DK35446-09 and R01 DK49545-01. The United Statesgovernment has certain rights in this invention.

BACKGROUND OF THE INVENTION

This invention relates to treatment of diabetes with synthetic betacells, and specifically to a method of utilizing non-islet cellscomprising a genetic construct that has a coding sequence for aproinsulin expressible in the cells in response to glucose levels. Theproinsulin synthesized in the cells is further processed into asecretable, active insulin.

Insulin is normally produced in and secreted by the beta cells of theislets of Langerhans in the pancreas. Mature insulin is a protein havingtwo polypeptide chains, A and B, held together by disulfide bonds. Theglucose responsive release of insulin from the beta cells is a complexevent including gene expression, posttranslational modification andsecretion. The initial protein product- and insulin precursor ispreproinsulin, a single polypeptide chain having an N-terminal signalsequence and an intervening sequence, the C-peptide, between the A and Bchains. The signal sequence is cleaved during transport from the roughendoplasmic reticulum to form proinsulin. The proinsulin is packagedinto secretory granules along with specific enzymes required for itsprocessing. Proinsulin folds into a specific three-dimensionalstructure, forming disulfide bonds. Mature insulin results from removalof the C-peptide. In beta cells, this function is catalyzed byendopeptidases that recognize the specific amino acid sequences at thejunction of the A chain and the C peptide (C-A junction) and at thejunction of the B chain and the C peptide (B-C junction). Matureinsulin, stored in secretory granules, is released in response toelevated blood glucose levels. The detailed mechanism of insulin releaseis not completely understood, but the process involves migration andfusion of the secretory granules with the plasma membrane prior torelease.

In normally functioning beta cells, insulin production and release isaffected by the glycolytic flux. Glucokinase and glucose transporter 2(GLUT-2) are two proteins that are believed to be involved in sensingchanges in glucose concentration in beta cells. A reduction in GLUT-2,which is involved in glucose transport, is correlated with decreasedexpression of insulin; loss of glucokinase activity causes a rapidinhibition of insulin expression.

Autoimmune destruction of pancreatic beta cells causes insulin-dependentdiabetes mellitus or Type I diabetes. As a consequence of partial orcomplete loss of beta cells, little or no insulin is secreted by thepancreas. Most cells, with the exception of brain cells, require insulinfor the uptake of glucose. Inadequate insulin production causes reducedglucose uptake and elevated blood glucose levels. Both reduced glucoseuptake and high blood glucose levels are associated with a number ofvery serious health problems. In fact, without proper treatment,diabetes can be fatal.

One conventional treatment for diabetes involves periodic administrationof injectable exogenous insulin. This method has extended the lifeexpectancy of millions of people with the disease. However, bloodglucose levels must be carefully monitored to ensure that the individualreceives an appropriate amount of insulin. Too much insulin, can causeblood glucose levels to drop to dangerously low levels. Too littleinsulin will result in elevated blood glucose levels. Even with carefulmonitoring of blood glucose levels, control of diet, and insulininjections, the health of the vast majority of individuals with diabetesis adversely impacted in some way.

Replacement of beta cell function is a treatment modality that may havecertain advantages over insulin administration, because insulin would besecreted by cells in response to glucose levels in the microenvironment.One way of replacing beta cell function is by pancreas transplantation,which has met with some success. However, the supply of donors is quitelimited, and pancreas transplantation is very costly and too problematicto be made widely available to those in need of beta cell function.

There have been many other proposed alternatives for beta cellreplacement, including replacing beta cell function with actual betacells or other insulin-secreting, pancreas-derived cell lines (Lacy, etal., Ann. Rev. Med., 37:33, 1986). Because the immune system recognizesheterologous cells as foreign, the cells have to be protected fromimmunoactive cells (e.g., T-cells and macrophages mediating cytolyticprocesses). One approach to protect heterologous cells is physicalimmunoisolation; however, immunoisolation itself poses significantproblems.

U.S. Pat. No. 5,427,940 issued to Newgard discloses another approach tobeta cell replacement. This patent describes an artificial beta cellproduced by engineering endocrine cells of the At-T-20 ACTH secretingcells. A stably transfected cell, At-T-20, is obtained by introducingcDNA encoding human insulin and the glucose transporter gene, i.e. theGLUT-2 gene, driven by the constitutive CMV promoter. The cell linealready expresses the correct isoform of glucokinase required forglucose responsive expression of the proinsulin gene. Although the cellline is responsive to glucose, it is secretagogue-regulated atconcentrations below the normal physiological range. Therefore, use ofthese cells in an animal would likely cause chronic hypoglycemia;furthermore, these cells are derived from a heterologous source and bearantigens foreign to the recipient host.

U.S. Pat. No. 5,534,404 issued to Laurance et al. discloses anotherapproach to obtaining a cell line in which insulin production issecretagogue-regulated. Subpopulations of beta-TC-6 cells having anincreased internal calcium concentration, a property associated withinsulin secretion, were selected using a cell sorter. After successivepassages, a subpopulation of cells that produce insulin in response toglucose in the physiological range (4-10 mM) was selected, and the cellswere encapsulated for therapeutic use in alginate bounded by a PAN/PVCpermselective hollow fiber membrane according to the method of Dionne(International Patent application No. PCT/US92/03327).

Valera et al., FASEB Journal, 8: 440 (1994) describes transgenic mousehepatocytes expressing insulin under the control of the PEPCK promoterdriven by P-enolpyruvate. The PEPCK promoter is sensitive to theglucagon/insulin ratio and is activated at elevated glucose levels. ThePEPCK/insulin chimeric gene was introduced into fertilized mouse eggs.Under conditions of severe islet destruction by streptozotocin (SZ), theproduction and secretion of intact insulin by the liver compensated forloss of islet function.

Despite these prior art attempts, there is a continuing need foralternative methods to conventional insulin therapy for the treatment ofdiabetes.

SUMMARY OF THE INVENTION

The present invention relates to a genetic construct that can be used toobtain glucose-inducible expression of active insulin in a host cell.The genetic construct permits glucose-regulated expression of proinsulinin the presence of higher than physiologic concentrations of glucose,but not at lower than physiologic glucose concentrations. The presentinvention further provides that the proinsulin encoded by the codingsequence of the genetic construct comprises an amino acid sequences thatallows the proinsulin to be converted into a secretable, active insulin.

In one aspect, the invention provides a genetic construct forglucose-inducible expression of active insulin in host cells. Theconstruct comprises (i) a coding sequence for a human proinsulin, thecoding sequence operably connected a promoter functional in the hostcell, wherein the proinsulin amino acid sequences corresponding to theB-C and C-A junctions of native human proinsulin are cleavable in thehost cell; (ii) a glucose responsive regulatory module located 5′ of thepromoter, the module having at least one glucose inducible regulatoryelement (GIRE) comprising a pair of CACGTG motifs linked by a five basenucleotide sequence; and (iii) a 5′ untranslated region (UTR), located5′ of the coding sequence and 3′ of the promoter, not nativelyassociated with the coding sequence for human proinsulin. A highlyadvantageous feature of the invention is that a 5′ UTR not nativelyassociated with the human proinsulin coding sequence is employed toreduce the formation of secondary structures that can lead totranslational pausing and reduced expression of preproinsulin.

In another aspect, the invention includes a method for obtainingglucose-regulated expression of active insulin in a mammalian subject,comprising the step of delivering into the subject a genetic constructaccording to the invention in an amount and under conditions effectiveto allow at least a portion the subject's cells to take up theconstruct. In a preferred embodiment, the genetic construct isintegrated into the genome of a suitable virus-derived vector infectivefor a target host cell for delivery into the subject.

In another aspect, the invention provides a method for regulating bloodglucose levels wherein insulin is secreted in response to glucose levelsby cells transformed by the aforementioned genetic construct.

Other advantages and a fuller appreciation of specific features of theinvention will be gained upon review of the following drawings anddetailed descriptions of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a genetic map of the pACCMV.plpA, an 8.8 kb plasmid containingthe cloning sites for the expression construct for proinsulin, and alsoseveral adenoviral genes;

FIG. 2A is a genetic map showing the insertion of the expressionconstruct in relation to various markers on the pACCMV.p.A plasmid; FIG.2B shows the order of genetic elements 5′ to 3′;

FIG. 3 is a genetic map of pJM17;

FIG. 4 is a genetic map showing the recombination of vectors pACCMV.plpAand pJM17 to yield the AdC/FAM construct;

FIG. 5 is a schematic diagram of the steps used to clone M2A and M2B;

FIG. 6 is a graph showing total insulin released from lysed Cos 7 cellstransfected with recombinant plasmids;

FIG. 7 is a graph showing intracellular and secreted insulin by Cos 7cells transfected with recombinant plasmids;

FIGS. 8A, 8B and 8C are graphs showing the production of insulinsecreted into medium by hepatocytes transfected with a constructcontaining one, two or three GIREs, respectively, as a function ofglucose concentration.

FIG. 9 shows blood glucose levels/for normal, treated diabetic anduntreated diabetic rats immediately prior to (time 0) and at varioustimes after oral administration of glucose.

FIG. 10 shows fasting blood glucose levels for normal, treated diabeticand untreated diabetic rats.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a method for producing insulin in a cellin which insulin is not natively produced comprising delivering into thecell a genetic construct comprising a nucleotide coding sequenceexpressible in the cells in response to increased glucoseconcentrations, the sequence encoding a proinsulin that can be processedinto active insulin in the host cell. Accordingly, one aspect of theinvention is a genetic construct containing a nucleotide sequenceencoding proinsulin operably connected to a promoter functional in thehost cell under control of one or more glucose inducible regulatoryelements (GIRE), which confer glucose-regulated control of transcriptionof the sequence. Specifically, the construct in accordance with thepresent invention includes (i) a promoter functional in the host cell;(ii) a coding sequence for a human proinsulin, the coding sequenceoperably connected to the promoter, and wherein the proinsulin aminoacid sequences corresponding to the B-C and C-A junctions of nativehuman proinsulin are cleavable in the host cell; (iii) a glucoseresponsive regulatory module located 5′ of the promoter, the modulehaving at least one GIRE comprising a pair of CACGTG motifs linked by afive base sequence; and (iv) a 5′ untranslated region (UTR), located 5′of the coding sequence, not natively associated with the coding sequencefor human proinsulin.

By a “coding sequence for human proinsulin,” it is meant a sequence thatencodes an insulin precursor capable of being processed into a proteinhaving the biological activity of insulin (“active insulin”). As usedherein, “active insulin” is a protein, the in vivo expression of whichis correlated with a reduction in blood glucose levels. The codingsequences disclosed in the Examples herein encode preproinsulin, whichincludes a signal peptide that is important in the transit of thenascent polypeptide. However, for the sake of simplicity, a “codingsequence for human proinsulin” will be used throughout, because thesignal peptide is removed from preproinsulin during or very shortlyafter translation to form proinsulin.

In the Examples below, hepatocytes and Cos 7 cells were used to evaluatethe glucose-inducible expression of a proinsulin coding sequence underthe control of a glucose responsive regulatory module. Hepatocytes werechosen as a candidate for glucose-regulated expression of insulinbecause hepatocytes contain GLUT-2 and glucokinase, enzymes believedimportant in glucose “sensing.” However, it is reasonably expected thatother cell types may also be suitable in the practice of the presentinvention.

Another advantage of using hepatocytes for insulin production is thatthese cells contain the endopeptidase furin. Furin is believed to cleaveproinsulin at its B-C junction, although it is very inefficient atcleaving the C-A junction. As explained hereinbefore, cleavage at bothsites is necessary for excision of the C-peptide, which is required forconversion of proinsulin to active insulin. A single point mutation(T²⁵⁷ to G) in the human insulin open reading frame (ORF) converts theamino acid sequence LQKR (SEQ ID NO:18) to RQKR (SEQ ID NO: 19), whichresults in a modified C-A junction that can be cleaved by furin. Thus,the proinsulin protein can be processed into insulin in cells having anendopeptidase capable of cleaving the modified C-A junction, i.e.insulin (M1).

As described in the Examples below, modification of the coding regionfor human insulin specifying the B-C junction of native insulin convertsthe amino acid sequence of proinsulin KTRR (SEQ ID NO:22) to a cleavableB-C junction having a different sequence RTKR (SEQ ID NO:23) i.e.insulin (M2). Modification of both junctions, C-A and B-C, facilitatesconversion of proinsulin to active insulin.

In the Examples, various combinations of different glucose inducibleregulatory elements were constructed and evaluated for their ability toallow glucose-induced transcription of insulin mRNA. As used herein, a“glucose inducible regulatory element” (GIRE) refers to a polynucleotidesequence containing at least one pair of perfect CACGTG motifs, eachmember of the pair separated from the other by a sequence of five basepairs. A “glucose responsive regulatory module” contains one or moreGIREs. The regulatory elements were inserted 5′ of the 5′ untranslatedregion of human proinsulin gene and then cloned into an adenovirusvector which was used to transfect hepatocytes. As the Examples belowdemonstrate, the GIREs provide transcriptional regulation of insulinmRNA in hepatocytes in response to physiologically relevant glucoseconcentrations.

In the Examples below, a rat albumin promoter was used as the promoterin the tested constructs (SEQ ID NO:24). However, any suitable promoterthat is functional in the intended target cell could be employed. Thepromoter is preferably a relatively strong constitutive promoteroperative in the host cell of choice, and responsive to the regulatorymodule located on its 5′ end.

The 5′-untranslated region (5′-UTR) of the human proinsulin genecontains an inverted repeat capable of forming a stem-loop in theinsulin mRNA, the formation of which inhibits translation. To minimizereduced translation by formation of secondary structures caused byintramolecular base-pairing of the 5′ UTR, the 5′-UTR of the proinsulingene was replaced with the 5′-UTR of rat albumin (bases 153-188 of thesequence published as GenBank Accession No. M16825, SEQ ID No.: 24) inits native orientation. Those skilled in art will appreciate that other5′-UTRs may be substituted for the rat albumin 5′-UTR. It is importantthat adequate spacing (about 25 base pairs) be provided between theregulatory module and the transcriptional start site, and that the 5′UTR does not result in secondary structure that will interfere withbinding to and processing by ribosomes.

The 3′-UTR of human preproinsulin affects the half life of mRNA, andhence, the production of protein over time. Two different constructswere prepared to include the rat albumin 5′-UTR (bases 153-188 ofGenBank Accession No. M16825; SEQ ID NO:24), a human insulin ORF, andvarying lengths of 3′-UTR. Two constructs, designated M2A and M2B,differ only in that M2A terminates at the stop codon of the open readingframe, whereas M2B contains an additional 18 bases after the stop codonin the 3′UTR of human proinsulin. The two constructs M2A and M2B wereused to evaluate insulin expression in Cos 7 host cells.

Insulin production was compared from constructs containing regulatorymodules having one (SEQ ID NO:8), two (SEQ ID NO:9) or three (SEQ IDNO:10) GIRES in combination with the rat albumin promoter, rat albumin5′ UTR and proinsulin sequence M2B. The complete sequences of theseconstructs, which were inserted into adenovirus vectors, are listed asSEQ ID NO:11, SEQ ID NO:12, and SEQ ID NO:13, respectively. Hepatocytestransfected with the adenovirus vector containing a regulatory modulehaving one GIRE demonstrated relatively low levels of insulinproduction, whereas hepatocytes transfected with the vectors havingregulatory modules containing two or more GIREs demonstrated high levelsof insulin production in response to physiologically relevant levels ofglucose. It is expected that the baseline production of insulin willplateau with increasing numbers of GIREs. Furthermore, the constructcontaining a module with three GIRES was more responsive to 10 mMglucose than was the construct containing two GIREs.

The regulatory module for glucose-inducible transcription in the presentinvention is a synthetic oligonucleotide having at least one GIRE, eachGIRE containing two operative regulatory motif segments CACGTG separatedby a nucleotide linker segment, conveniently of the sequence GGCGC.Preferably, the regulatory module contains from 2 to 8 GIREs, and mostpreferably, the module contains from 3 to 5 GIREs. Additional GIREs arenot expected to result in further increases in transcription. Moreover,GIREs in excess of five are not expected to interfere withglucose-inducible regulation.

One viral vector suitable for use in the method of the invention is ahelper-free, replication-defective vector, derived from the adenovirusgenome, and described in Newgard, et al., “Glucose-Regulated InsulinSecretion,” in Molecular Biology of Diabetes, eds. Draznin, et al.,Humana Press 1992. FIG. 14 diagram the genetic components andconstruction of the vector containing the genetic construct. It isexpected that other transducing systems may also be suitable for thepresent invention. For example, it is expected that the integrativeretroviral systems and another helper-free recombinant adenoviral systemdisclosed in U.S. Pat. No. 5,436,146 issued to Shenk et al. may beuseful.

Viral-derived vectors have the advantage that delivery to target cellsis relatively straightforward and can be accomplished in vivo. However,it should be appreciated that the constructs of the present inventioncould also be used to transfect cells ex vivo, which could then bereintroduced into a mammalian subject in vivo.

In in vivo studies, it was found that streptozotocin-treated (SZ)diabetic rats whose livers were injected with a viral vector containingthe genetic construct in accordance with the present invention were ableto control blood glucose levels comparable to normal rates, whileuntreated SZ-diabetic rats had blood glucose levels four fold higherthan the treated SZ-diabetic and normal rats. It was also found thatfasting blood glucose levels were significantly reduced in theSZ-diabetic rats compared to the untreated SZ-diabetic rats and that theblood glucose levels were reduced in a viral dose-dependent manner. Asshown in the Examples, the level of blood glucose reduction inSZ-diabetic rats is a function of the dose of the viral vector deliveredto the rat.

The viral dose employed in the Examples below was 1×10¹² or 2×10¹² pfuper rat. The virus was delivered in a phosphate buffered saline carrier.It is envisioned that the present invention may be practiced usingdifferent doses or carriers. It is well within the ability of oneskilled in the art to determine optimal doses and to select suitablecarriers. In the Examples below, the virus was delivered by directinjection into the liver. In addition to direct injections, the virusmay be administered by delivery into an in-dwelling catheter placed inthe hepatic portal vein.

In the Examples below, rats were used for in vivo studies. Rats are thepreferred model system for studying diabetes in humans. It is reasonablyexpected that the present invention may be employed to obtain expressionof insulin in diabetic humans as well.

It will be apparent to one skilled in the art that any structural genefor which glucose-modulated control is desired may be inserted into thegene construct using standard molecular biological techniques andexpressed in a suitable host cell. The glucose regulatory module of thepresent invention may be used to prepare a genetic construct suitablefor restoring glucose-mediated expression of proteins implicated in anumber of metabolic diseases.

The following nonlimiting examples are intended to be purelyillustrative.

EXAMPLE 1 Isolation of Proinsulin Coding Sequences

Proinsulin cDNA was prepared by extracting total RNA from normal humanislet cells, isolating the mRNA fraction and using it as a template toconduct an oligo (dT)₁₅ primed reverse transcription reaction. InsulincDNA (−28 bp443 bp) was amplified using sense and antisenseoligonucleotides designated TA423 (SEQ ID NO:1) and TA413 (SEQ ID NO:2)which include restriction sites for KpnI and SalI, respectively.Alternatively, cDNA can be isolated according to the methods describedin Bell, et al., Nature, 282:525 (1979), using the primers disclosedtherein, but incorporating restriction sites compatible with theselected cloning vehicle.

The amplified cDNA fragment (−28 bp-443 bp) containing the entire codingsequence of human insulin and portions of the 5′-UTR and the 3′-wassubcloned into pBlueScript SK+ (Shon, et al., Nuc. Acids Res., 16: 7583,1988).

EXAMPLE 2 Amplification of Rat Albumin Promoter

A sequence comprising nucleotides 1-184 of the rat albumin (Heard, etal., Mol. Cell. Biol., 7: 2425-2434, 1987, incorporated herein byreference) was obtained by PCR amplification with synthetic primersusing rat genomic DNA as the template DNA. The primers, which containEcoRI and KpnI restriction sites, were designated TA420 (SEQ ID NO:6)and TA421 (SEQ ID NO:7). The amplified rat albumin promoter fragment waspurified and incubated under suitable conditions with Kpn I and Eco RI,and ligated to linearized pBlueScript DNA having compatible ends. Thesequence (SEQ ID NO:24) was verified by conventional sequencingtechniques.

EXAMPLE 3 Generation of a Mutant Insulin with Cleavable C-A and B-CJunctions

A mutation that changes the codon specifying Leu to a codon specifyingArg at position 62 was made using standard in vitro mutagenesis. Thesense oligonucleotide TA403 (SEQ ID NO:3), which includes a pointmutation corresponding to the desired change in the target region, andoligonucleotide TA413 (SEQ ID NO:2) were used as primers to amplify onesegment of insulin sequence. Similarly, an antisense oligonucleotideTA404 (SEQ ID NO:4) containing the Leu to Arg mutation was used with theoriginal insulin sense oligonucleotide TA423 (SEQ ID NO:1) to amplifythe second fragment of modified insulin (M1). The two fragments thusproduced were purified, combined, and used as template DNA to amplifythe modified insulin M1 using oligonucleotides TA423 and TA413 asprimers. The C-A modified insulin M1 was ligated to pBlueScript SK+,linearalized with KpnI and SalI, or used as a template for generating asecond mutant containing a mutation in the B-C junction. Using primersTA414 (SEQ ID NO:20) and TA415 (SEQ ID NO:21), the insulin M1 sequencewas subjected to in vitro mutagenesis to obtain mutations in the codingregion specifying the B-C junction (KTRR; SEQ ID NO:22) to obtain asequence that encodes a B-C junction having the sequence RTKR (SEQ IDNO:23), i.e. insulin (M2).

EXAMPLE 4 Generation and Cloning of Proinsulin Genetic Constructs in thePlasmid pACdeltaCMV

The plasmid pACCMV.pLpA (FIG. 1) was used as a vector for generation ofreplication defective recombinant adenovirus containing genes ofinterest. The CMV promoter was removed by digesting plasmid DNA withSalI and partially digesting the DNA with the enzyme NotI. The 8.3 kbpiece of vector DNA (pACdeltaCMA) lacking the CMV promoter was isolatedby agarose gel electrophoresis and by gel purification.

Constructs containing either the C or F module were prepared. The Cmodule (SEQ ID NO:14) is based on the published sequence of S14 (Shih &Towle, J. Biol. Chem. 269: 9380-9387, 1994). The F module (SEQ ID NO:5)is found in the fatty acid synthetase gene. An oligonucleotide paircorresponding to a glucose responsive regulatory module C or F wascombined with gel purified EcoRI-KpnI rat albumin promoter and KpnI-SalIInsMI DNA fragments, and ligated into the above-described plasmid vectorpACdeltaCMV. Two different constructs containing either module C ormodule F were obtained. Each of the two constructs was co-transfectedwith the plasmid pJM17 into the host HEK 293 cell line to generaterecombinant replication-defective adenovirus constructs, namely AdCAM1and AdFAM1 (see FIG. 5).

EXAMPLE 5 Expression of Insulin in Hepatocytes at Various GlucoseConcentrations

Rat hepatocytes were prepared by in situ perfusion of 0.5 mg/mLcollagenase in supplemented balanced Hank's solution as described inKreamer et. al. In Vitro 22: 201-211, 1986. The viability of isolatedhepatocytes was 90% or higher.

Six collagen coated 60 mm plates, each containing 1×10⁶ hepatocytes,were transfected with AdCAM1 or AdFAM1 (5×10⁷ pfu/plate). Transfectedhepatocytes were exposed to three concentrations of glucose, 3.3 mM, 5.6mM and 27.5 mM, in RPMI supplemented with 10% fetal calf serum, 30 μg/mLproline, 5 μg/mL insulin, 5 μg/mL transferrin and 5 μg/mL selenium, andincubated at 37° C. After 36 hours, RNA was isolated from hepatocytes onone of two plates used at each tested glucose concentration. Theduplicate plate was used to evaluate cell viability. Variation inhepatocyte viability of cells exposed to different concentrations ofglucose was less than 10%.

10 μg of RNA from each sample was separated electrophoretically on aformaldehyde-2% agarose gel, transferred to a Nylon membrane,UV-crosslinked, and hybridized with digoxygenin-labeled insulin cRNA.Detection of the membrane-bound probe was performed bychemiluminescence. The results were recorded as multiple exposures onX-ray films for various lengths of time and quantitated by digital imageanalysis.

Northern analysis revealed an intense signal migrating at the positionpredicted by the size of the proinsulin transcript (1.35 kb). This bandwas observed only in transduced hepatocytes cultured in the presence of27.5 mM glucose. There appeared to be no induction of the proinsulingenetic construct over background in hepatocytes exposed to 3.3 or 5.5mM glucose. The transfected hepatocytes express insulin mRNA only inresponse to glucose concentrations that fall within or above thephysiological range. Strong induction is seen at glucose concentrationsof greater than 5.5 mM.

Results of Northern analysis show that both glucose regulatory modules Cand F confer glucose dependent inducibility to the same degree, althoughthe AdFAM construct using the F module appears to be somewhat moreresponsive. Hepatocytes transfected with AdCMV-Ins, in which theproinsulin coding sequence is under control of the constitutive CMVpromoter, generates RNA of the distinctive size without regard toglucose concentration.

Results of RNA quantitation by phosphoimaging are summarized in Table 1.There was only a slight difference in relative expression between 3.3and 5.6 mM glucose, in contrast to a 3.06-fold increase in relativeexpression at glucose concentrations of 27.5 mM. TABLE 1 RelativeTranscription of Insulin mRNA in Hepatocytes Normalized hlns HIns mRNAGlucose mRNA (hIns (Relative* (mM) HIns mRNA 18s RNA mRNA/18s RNA)Expression) 3.3 81074 56 787 0.91 5.6 51039 33 865 1.00 27.5 201056 402645 3.06*For the sake of comparison, the normalized amount of insulin mRNAexpressed at euglycemic level (5.6 mM glucose) is arbitrarily assumed tobe one.

EXAMPLE 6 Cloning of Insulin Construct with Rat Albumin 5′ UntranslatedRegion and Truncated 3′ Untranslated Region

The proinsulin coding sequences of Example 3 were further modified byeliminating the 5′ untranslated region of human insulin mRNA andreplacing that region with the 5′ untranslated region of rat albumin(bases 153-188 as published in GenBank Accession No. M16825, hereinincorporated by reference; SEQ ID NO:24). This modification wasaccomplished by PCR amplification of hInsM2 using three oligonucleotideprimers. Synthesis of one strand was performed using the oligonucleotideTA455 (SEQ ID NO:15) which comprises a KpnI recognition site, bases153-188 of the albumin promoter corresponding to the 5′-untranslatedregion of albumin and a sequence corresponding to human proinsulin mRNA(starting with the first base of the codon specifying the first aminoacid), TA452 (SEQ ID NO: 16), which is complementary to the sequencethat terminates at the end (base 392) of the insulin open reading frame,or TA454 (SEQ ID NO:17), which is complementary to the sequence thatends 18 bases after the termination codon of the insulin ORF. TA452 andTA454 each contain a Sal I restriction site to facilitate cloning of theproducts described in Example 1. The amplification product of TA455 andTA452 was designated M2A, and the amplification product of TA455 andTA454 was designated M2B.

Following amplification, the chimeric sequences M2A and M2B weresubcloned without their promoter sequences by digesting the amplifiedDNA with KpnI and by ligating to KpnI-EcoRV-digested plasmid vectorpcDNA3 (Invitrogen, Madison, Wis.) which contains a CMV promoter, asshown schematically in FIG. 5. Following ligation, the plasmids wereused to transform competent E. coli DH5α cells. Additional plasmid DNAwas isolated from transformants, and plasmid DNA was introduced into Cos7 cells as described below.

EXAMPLE 7 Secretion of Insulin from COS 7 Cells Transfected with InsulinConstructs Containing the 5′-Untranslated Region of Rat Albumin

Cos 7 cells were used to test the ability of the constructs described inExample 3 to synthesize and secrete insulin. The TRANS IT™ transfectionreagent (Pan Vera Corp., Madison, Wis.) was used to transfect the Cos 7cells with plasmids containing the M2A and M2B mutants for transientexpression. A four-hour period of incubation for transfection wasfollowed by an overnight incubation of the cells in fresh DMEMsupplemented with 10% fetal calf serum. The medium was then changed andthe plates incubated for two days in medium containing either 10% or 5%fetal calf serum. The medium was collected and the cells were harvestedseparately. The cells were lysed in Tris-buffered saline (pH 7.6)containing 1% NP-40, a nonionic detergent, and protease inhibitors(trypsin inhibitor and PMSF). Both the medium and cell lysate wereanalyzed for the presence of insulin by antigen capture ELISA.

The results indicate that both M2A and M2B direct the synthesis ofsecretable insulin (FIGS. 6 and 7). Insulin production was higher in Cos7 cells transformed with the M2B construct. It is also apparent that themajority of the synthesized insulin is secreted (FIG. 7). Control cellstransformed with the vector pcDNA 3 with no insert did not produceinsulin.

EXAMPLE 8 Construction of Chimeric Proinsulin Sequences Containing Oneor More Glucose Inducible Regulatory Element and Having the 5′ UTR ofRat Albumin

Three chimeric human insulin constructs in adenovirus, containing one,two or three GIRE units, an albumin promoter and a coding sequence forhuman proinsulin (including two mutations to aid furin-mediatedprocessing of proinsulin to insulin) were prepared.

The general strategy of assembling the HIns constructs was essentiallythe same as described above. The sense and antisense oligonucleotidescorresponding to one or two GIREs were chemically synthesized. Thesequences of the sense oligonucleotides are shown in SEQ ID NO:8 and SEQID NO:9. Each set of oligonucleotide pairs was designed to have arecognition sequence for NotI and EcoRI at the 5′-and 3′-ends,respectively. An additional pair of oligonucleotides corresponding toone GIRE was made to contain EcoRI and XbaI sites on the 5′ and 3′ ends,respectively. The original sense oligonucleotide [TA420 (SEQ ID NO:6) orTA421 (SEQ ID NO:7)] was used for amplification of rat albumin promotercontaining an EcoRI site and an XbaI site. A construct containing threeGIREs (SEQ ID NO:10) was prepared using the oligonucleotides shown inSEQ ID NO:8 and SEQ ID NO:9 and standard molecular biologicaltechniques.

The rat albumin promoter sequence bases 1-184 of the published sequence(Accession No. M16825, SEQ IS NO: 24) described earlier was extended byPCR to include the entire 5′-untranslated region of rat albumin. Asequence encoding the human proinsulin (M2B) containing point mutationsin the sequences corresponding to the B-C and C-A junction of proinsulinobtained from constructs previously described was modified to eliminatethe 5′-untranslated region arising from hIns cDNA by PCR. The twofragments of DNA were joined together by overlap extension in a PCRreaction. The product of this reaction contains (5′->3′) albuminpromoter, 5′-UTR of albumin and a coding sequence for human proinsulincomprising a modified C-A junction, i.e., a T->G mutation at base 257 ofthe open reading frame to yield an arginine residue at amino acidresidue 62 of proinsulin in place of the leucine residue of nativeproinsulin (LQKR to RQKR) and a modified B-C junction of nativeproinsulin, i.e., KTRR to RTKR. This DNA fragment, which contains EcoRIand SalI recognition sequences at the 5′ and 3′-ends, respectively, wasdigested with the two enzymes, mixed with the annealed pair ofoligonucleotides corresponding to one or two GIREs, described above, andligated to linearized pACdeltaCMV DNA.

EXAMPLE 9 Glucose-Inducible Synthesis of Insulin in Hepatocytes

Vectors comprising insulin constructs comprising one, two or three GIREswere individually mixed with the plasmid pJM17 and the mixture of thetwo plasmid DNAs cotransfected into HEK 293 cells to generaterecombinant replication-defective adenovirus (as described in Example 7,above). The sequence of each construct was confirmed by standardsequencing methods. Freshly prepared hepatocytes were plated oncollagen-coated 30 mm plates and transfected with adenovirus containinginsulin construct with one (Ad1SAM2B), two (Ad2SAM2B) or three(Ad3SAM2B) GIREs at a multiplicity of infection (MOI) of four. Thesequences of each insert for Ad1SMA2B, Ad2SAM2B and Ad3SAMB are shown inSEQ ID NO:11, SEQ ID NO:12, and SEQ ID NO:13, respectively. The culturemedium was changed 16 h post-transfection, with medium containing 2.5,5.6, 10 or 27.5 mM glucose. The insulin secreted into the medium wasassayed 32 hours after media change, by antigen capture ELISA (Table 4;FIG. 8A-C).

A glucose-dependent increase in the secreted insulin from transducedhepatocytes is clearly seen when the gene construct contains either twoGIREs (FIG. 8B) or three GIREs (FIG. 8C). However, glucose dependentexpression and secretion of insulin in cells transfected with Ad1SMA2B,which contains a single GIRE, was minimal (FIG. 8A). Furthermore, theconstruct containing three GIREs, in addition to a higher maximalinduction at 27.5 mM glucose (approximately 9-fold increase over thelevel at 2.5 or 5.6 mM glucose as opposed to 6.5 fold increase in thecase of construct with two GIREs under identical conditions), alsoshows >2 fold increase in insulin secretion at 10 mM glucose. TABLE 4Amount of insulin secreted (ng/ml) by hepatocytes transfected withvectors containing one, two, or three GIREs in response to glucosechallenge. Glucose, mM Ad1SAM2B Ad2SAM2B Ad3SAM2B 2.5 4.97 ± 1.09 9.09 ±2.27 9.98 ± 1.37 5.6 5.12 ± 1.26 10.72 ± 2.30  10.80 ± 1.57  10.0 3.2 ±1.8 13.2 ± 2.4  22.8 ± 4.1  27.5 12.75 ± 2.05  67.16 ± 10.24 90.33 ±19.80

EXAMPLE 10 Insulin Transcription of a GIRE Construct in Response toPhysiological Levels of Glucose as a Function of Time

Collagen coated 60 mm plates or dishes, each containing 1×10⁶hepatocytes, were transfected with Ad2SAM2B at a rate of 3.5×10⁶pfu/plate Hepatocytes receiving no virus, or virus encodingbacterial-galactosidase were included as controls. Hepatocytes were thenexposed for 16 h to 5.6 mM glucose in RMPI supplemented with 10% fetalcalf serum, 30 μg/mL proline, 5 μg/mL insulin, 5 μg/mL transferrin and 5μg/mL selenium, at 37° C. The plates containing transfected cells werethen divided into two groups; one group received fresh medium containing5.6 mM glucose, the second group received fresh medium with 27.5 mMglucose. From each of these two groups, individual plates were removedafter 30 min, 1 h, 2 h, 4 h, 8 h, and 16 h, the medium decanted, and thecells frozen in liquid nitrogen. Total RNA was extracted, separatedelectrophoretically and analyzed for hIns mRNA by northern blotting, asdescribed above.

The results of northern blotting showed that hepatocytes transfectedwith Ad2SAM2B and exposed to 27.5 mM glucose contained detectable levelsof hIns mRNA after 30 min, and that the hIns mRNA levels increasedthereafter in a time-dependent manner. At the normal glucose level (5.6mM), the signal was much lower. Quantitation of the bands revealed thathIns mRNA levels were approximately 10-fold higher in hepatocytesexposed to glucose concentrations of 27.5 mM than in hepatocytes exposedto glucose concentrations of 5.6 mM.

These data demonstrate that the vector construct containing two GIRESinitiates transcription in response to elevated glucose levels in a timeframe comparable to islet cells. Insulin mRNA production is increased inthe presence of 5.6 mM glucose, the steady state concentration ofglucose in the bloodstream, but is stimulated at relatively highconcentrations of glucose (27.5 mM).

EXAMPLE 11 Insulin Synthesis by Hepatocytes Transfected with ConstructContaining Two GIREs

Freshly prepared rat hepatocytes were transfected with two differentadenovirus constructs containing the M1 mutated proinsulin sequence:AdSAM1 (containing the rat albumin promoter modified to contain twoGIREs) and AdCMVInsM1 (containing the constitutive and highly active CMVpromoter). Hepatocytes transfected with AdCMV.β-Gal and untransfectedhepatocytes were used as controls. Four plates of hepatocytes weretransfected with each adenovirus preparation; two plates were exposed tothe low (3.3 mM) or high (27.5 mM) glucose concentrations. After 36hours, hepatocytes were exposed for 16 hours to 5.6 mM or 27.5 mMglucose in RMPI supplemented with 2 mg/mL bovine serum albumin withleucine omitted, 30 μg/mL proline, 5 μg/mL insulin, 5 μg/mL transferrinand 5 μg/mL selenium, at 37° C.

Following a 6 h leucine depletion, a 2 mL aliquot of the low or highglucose containing defined medium was added to appropriate plates. Foreach tested recombinant adenovirus, one plate for each glucoseconcentration received 0.2 mCi ³H-leucine (500 Ci/mmole). The remainingplate received the equivalent amount of unlabelled leucine and at theend of all incubations it was used for viability determination.

The leucine incorporation was carried out for 16 h, followed by a 4 hchase with unlabeled leucine. The culture medium was aspirated, celldebris removed, and the supernatant analyzed for secreted insulin. Thecells on each plate were lysed with 0.8 mL solution containing 20 mMTris-HCL buffer at pH 7.6, 2 mM EDTA, 5 μg/mL trypsin inhibitor, 50 μMphenylmethane sulphonyl fluoride (PMSF) and 1% Triton-X100. The lysatewas centrifuged at 16,000×g for 10 min in a microcentrifuge, the pelletdiscarded, and the supernatant solution used for analysis of labeledintracellular products.

Each assay included 0.8 mL of culture supernatant or 0.4 mL of celllysate supernatant. To minimize non-specific precipitation of labeledproteins, cultures were pre-treated with Staphylococcus aureus in theabsence of specific antibodies. A 50 μL aliquot of a 10% suspension offormalin-fixed Staphylococcus cells (Calbiochem) was added to each tube;tubes were incubated at room temperature for 30 min with continuousmixing, centrifuged (4 min, 16,000×g), and the supernatant was used forfurther analysis. To immunoprecipitate insulin and insulin-relatedproducts, 2.5 μL of polyclonal guinea pig anti-human insulin (SigmaChemical Co.) was added to the supernatant solution, mixed and kept atroom temperature for 45 min, followed by addition of Staphylococcuscells, 30 min incubation and centrifugation as described above. Thesupernatant was discarded, and the pellet washed 4-5 times with 1 mL of20 mM Tris-HCl at pH 7.6, 0.15 M NaCl and 0.1% Triton X-100. To controlfor sample to sample variation, a 2 μL aliquot of rabbit anti-ratalbumin polyclonal antiserum was included along with anti-insulinantiserum to a series of duplicate samples treated as described above toco-precipitate human insulin and endogenous rat albumin.

Each pellet was suspended in a 40 μL aliquot of a solution containing 60mM Tris-HCl at pH 6.8, 1.2% SDS, 2% P-mercaptoethanol, heated at 100° C.for 4 min, centrifuged, and the supernatant analyzed bypolyacrylamide-SDS gel electrophoresis. Specificity of theimmunoprecipitated material was established by the use of control cellstransduced with β-galactosidase and untransfected cells. The identity ofthe immunoprecipitated material was confirmed in a separate set of testsamples to which unlabeled insulin or rat serum was added to providecompetition with labeled insulin or albumin respectively, and tubesprocessed simultaneously.

The optimum gel system for resolution of insulin B and A chains and ratalbumin was found to be an SDS/Tris-Tricine 10-20% linear polyacrylamidegradient based on the description of Schagger and Jagow (Anal. Biochem.166:368-379, 1987). A 15 μL aliquot of SDS-BME-treatedimmunoprecipitated material from each sample was resolved on the gelalong with peptide size markers from BioRad. The gels were fixed,stained, destained, soaked in “Amplify” solution (Amersham), dried undervacuum, and exposed to X-ray film at −80° C.

The results showed the presence of an anti-insulin antibody-binding bandin cell extracts of hepatocytes transduced with AdSAM1 (glucoseinducible) and AdCMV.InsM1 (constitutive). AdSAM1 contains two glucoseinducible regulatory elements coupled to the rat albumin promoter, andAdCMV.InsM1 contains the cytomegalovirus immediate/early promoter. WhenAdSAM1 was used, the insulin band appeared only in the hepatocytesexposed to high glucose (27.5 mM) and was not evident in cells exposedto low glucose (3.3 mM). In contrast, cells transfected with AdCMV.InsM1and exposed to 3.3 mM or 27.5 mM glucose produced insulin in roughlyequal amounts.

The size of the insulin positive band was determined to be 7,700Daltons, which differs somewhat from the sizes of mature insulin B and Achains. The size of rat albumin was determined to be 67,000 Daltons,which compares favorably with the known size. Band signals wereessentially eliminated in samples in which unlabelled insulin or albuminwas added. Densitometry revealed that insulin expression in cellstransfected with AdSAM1 and exposed to high glucose concentrations wasonly about 20-fold lower than in cells in which insulin expression isdriven by the constitutive promoter CMV, one of the strongest knownpromoter in most in vivo and ex vivo mammalian systems.

These data demonstrate the synthesis of insulin in response tophysiological levels of glucose in hepatocytes transfected with a vectorcontaining the proinsulin coding sequence under the control of twoGIREs. At 3.3 mM glucose, there is no detectable synthesis of insulin;at 27.5 mM glucose, insulin synthesis is readily detectable. By addingtwo GIREs to the vector, which provide an additional control mechanismat the transcriptional level, the synthesis of insulin is correctlyregulated in the appropriate physiological range. Synthesis of insulinmRNA and insulin are increased at glucose concentrations exceeding 5.6mM and are not synthesized or are synthesized at very low levels incells exposed to glucose concentrations of 5.6 mM. This feature makesvectors containing GIREs suitable for treating Type 1 diabetes.

EXAMPLE 12 Glucose Tolerance Testing of Normal, Treated, or UntreatedDiabetic Rats

Lewis rats (Harlin) fed an ad lib diet of Purina rat chow were fastedovernight, treated with 80 mg/kg streptozotocin (SZ) intravenously(i.v.) to induce a diabetic state, and injected with 1×10¹² pfu/rat ofAd3SAM2B using phosphate buffered saline (10 mM Na phosphate, 0.15 mNaCl pH 7.5) as the vehicle Injections were made at three to fourdifferent sites in the liver. Controls included untreated SZ-diabeticand normal rats. At ten days post infection, the animals were fastedovernight and fed glucose at a rate of 2 g glucose/kg body weight. Bloodwas collected from the rats just prior to and at various times after theglucose feeding to determine blood glucose levels. FIG. 9 shows theglucose levels as a function of time for treated SZ-diabetic, untreatedSZ-diabetic, and normal rats.

The results demonstrate that blood glucose levels of treated SZ-diabeticand normal rats were comparable just prior to and two to three hoursafter oral glucose dosing. In contrast, glucose levels in untreatedSZ-diabetic rats were about four fold higher than the treated and normalrats at these time point, and the peak glucose level was approximatelytwo-fold higher than that of the treated SZ-diabetic rat. Similarresults were obtained on the 7^(th) day after gene therapy.

EXAMPLE 13 Kinetics of Blood Glucose Reduction in Normal, Untreated orTreated Diabetic Rats

Lewis rats (Harlan) were fasted overnight and treated intravenously(i.v.) with 80 mg/kg SZ. Three days after the SZ treatment, rats wereinjected at three to four different sites in the liver with Ad3SAM2B ata rate of either 1×10¹² pfu or 2×10¹² pfu using phosphate bufferedsaline (10 mM Na phosphate, 0.15M NaCl, pH 7.4). Fasting blood glucoselevels for normal and for untreated or for treated SZ-diabetic rats weremeasured following overnight fasts for 20 days, and the results areshown in FIG. 10. The grey line and the shaded area represent thefasting blood glucose levels of normal control rats (mean ±SD) The10-day average blood glucose (mean ±SD) of each group is shown to theright of each curve.

The results demonstrate that insulin gene therapy in accordance with thepresent invention significantly reduced fasting blood glucose levels ofdiabetic rats. The reduction in blood glucose levels was viraldose-dependent.

In summary, the present invention provides a method forglucose-regulated production of active insulin in non-islet cells inwhich insulin is not naturally produced by providing the cells with agenetic construct containing a nucleotide sequence encoding proinsulinoperably connected to a promoter functional in the cell under thecontrol of one or more glucose inducible regulatory elements. Glucoseregulation by insulin so produced is maintained in the physiologicalrange.

While the present invention has now been described and exemplified withsome specificity, those skilled in the art will appreciate the variousmodifications, including variations, additions, and omissions, that maybe made in what has been described. Accordingly, it is intended thatthese modifications also be encompassed by the present invention andthat the scope of the present invention be limited solely by thebroadest interpretation that lawfully can be accorded the appendedclaims.

1. A genetic construct for glucose-regulated synthesis of active insulinin a host cell in which insulin is not natively produced, comprising apromoter functional in the host cell; a coding sequence for a humanproinsulin, the coding sequence operably connected to the promoter,wherein the protein encoded by the coding sequence comprises amino acidsequences corresponding to B-C and C-A junctions of native humanproinsulin that are cleavable in the host cell; a glucose responsiveregulatory module located 5′ of the promoter, the module having at leastone glucose inducible regulatory element comprising a pair of CACGTGmotifs linked by a five base nucleotide sequence; and a 5′ untranslatedregion not natively associated with the coding sequence for humanproinsulin, wherein the 5′ untranslated region is located 5′ of thecoding sequence and 3′ of the promoter.
 2. The genetic construct ofclaim 1, wherein the 5′ untranslated region is characterized by reducedformation of secondary structures by intramolecular base pairing,relative to the formation of secondary structures by the 5′ untranslatedregion natively associated with the coding sequence for human insulin.3. The genetic construct of claim 1, wherein the regulatory modulecomprises at least two glucose inducible regulatory element.
 4. Thegenetic construct of claim 1, wherein the proinsulin encoded by thecoding sequence comprises a modified C-A junction and a modified B-Cjunction, the modified C-A junction corresponding to a conversion of theamino acid sequence LQKR to RQKR and the modified B-C junctioncorresponding to the conversion of the amino acid sequence KTRR to RTKR5. A host cell comprising the genetic construct of claim
 1. 6. Thegenetic construct of claim 1, wherein the module comprises a sequenceselected from the group consisting of SEQ ID NO:9 and SEQ ID NO:10.
 7. Avirus infective for a host cell, the virus comprising a promoterfunctional in the host cell; a coding sequence for a human proinsulin,the coding sequence operably connected to the promoter, wherein theprotein encoded by the coding sequence comprises amino acid sequencescorresponding to the B-C and C-A junctions of native human proinsulinthat are cleavable in the host; a glucose responsive regulatory modulelocated 5′ of said promoter, the module having at least one glucoseinducible regulatory element comprising a pair of CACGTG motifs linkedby a five base nucleotide sequence; and a 5′ untranslated region notnatively associated with the coding sequence for human proinsulin,wherein the 5′ untranslated region is located 5′ of the coding sequenceand 3′ of the promoter.
 8. The virus of claim 7, wherein the host cellis a hepatocyte.
 9. A method for obtaining glucose regulated expressionof insulin in a suitable host cell, comprising delivering into the cella genetic construct cording to claim
 1. 10. The method of claim 9,wherein the host cell is a hepatocyte.
 11. The method of claim 9,wherein the genetic construct is delivered by exposing the cells to avirus infective for the cells, the virus comprising the geneticconstruct, under suitable conditions and at a multiplicity of infectionsufficient to allow at least a portion of the cells to be infected byvirus.
 12. A method for obtaining glucose-regulated expression of activeinsulin in a mammalian subject, comprising the step of delivering intothe subject a genetic construct according to claim 1 in an amount andunder conditions effective to allow at least a portion the subject'scells to take up the construct.
 13. The method of claim 12, wherein thecells are hepatocytes.
 14. The method of claim 12, wherein thedelivering step comprises exposing the subject to a virus infective forthe subject, the virus comprising the genetic construct, underconditions that allow at least a portion of the subject's cells to beinfected with the virus.
 15. The method of claim 12, wherein the subjectis diabetic.
 16. The method of claim 12, wherein glucose-inducedexpression of insulin correlates with a reduction in blood glucoselevels, relative to an similar control organism that does not receivethe genetic construct.
 17. A method for regulating blood glucose levelsin a mammalian subject in need thereof, comprising the step ofdelivering into the subject a genetic construct according to claim 1 inan amount and under conditions effective to allow at least a portion thesubject's cells to take up the construct.
 18. A genetic constructcomprising a promoter capable of being recognized by an RNA polymeraseof a host cell; a nucleotide sequence, operably connected to thepromoter, for a preproinsulin cDNA encoding a preproinsulin cleavableinto active insulin; a glucose responsive regulatory module located 5′of the promoter, the module having at least two glucose inducibleregulatory elements, each element comprising a pair of CACGTG motifslinked by a five base nucleotide sequence; and a 5′ untranslated regionnot natively associated with the coding sequence for human proinsulin,wherein the 5′ untranslated region is located 5′ of the coding sequenceand 3′ of the promoter.
 19. The genetic construct of claim 18 whereinthe glucose responsive regulatory module has at least three glucoseinducible regulatory elements.